One apparatus of the above kind is described in U.S. patent application Ser. No. 337,405, filed Apr. 13, 1989, now U.S. Pat. No. 4,916,774, and in the corresponding published French patent application No. FR 2 630 068A. As disclosed in those documents, the apparatus comprises a first, or cranked, arm, which is a driving arm mounted on a motor spindle and which has a pivot pin mounted close to the end of the cranked arm remote from the motor spindle. This pivot pin carries an eccentric knuckle piece, on which a second arm, or driven crank, is articulated by means of a socket which is carried by the second arm. The said knuckle piece is provided with a ratchet which includes a finger moveable in a direction substantially parallel to the axis of the pivot pin under the action of a spring. The ratchet is adapted to leave the knuckle piece free with respect to the first arm in a first direction of rotation of the latter, but to arrest the knuckle piece in the opposite direction of rotation. The assembly is such that, in normal operation, the first arm rotates in one direction for which the position of the eccentric knuckle piece remains constant with respect to one of the two elements consisting of the driven crank (the second arm) and the driving (first) arm, while during reversal of the direction of rotation of the driving arm, the knuckle piece is driven in rotation with respect to the said element. This causes a variation in eccentricity to occur, together with retraction of the windshield wiper.
To this end, the ratchet includes a radial arm which projects outwardly from the knuckle piece, while the socket has a recess for receiving the end of this arm.
Thus, in normal operation the knuckle piece is coupled in rotation with the socket by cooperation of the ratchet arm with the recess of the socket. In such an arrangement, the driven arm and the driving arm arranged to perform, relative to each other, a "universal" movement through the joint described above, which essentially a ball and socket type or knuckle joint, in which this movement consists essentially of rotational movement associated with inclination or tilting of the two arms with respect to each other.
The availability of this tilting movement is limited by the fact that in normal operation, the ratchet arm cooperates risk during severe tilting of coming into contact with the end of the said finger. This can cause fracture and therefore render the coupling inoperative. Similarly, in the retracted position of the wiper, the ratchet finger is engaged in the space lying between the driving arm and the socket, so as largely to occupy this space. In this position, the driven arm can only tilt in one direction, opposite to that in which the ratchet arm lies. In the opposite case, this arm presents an obstacle to the tilting movement.
Such an obstacle introduces the risk of malfunctioning occurring in the assembly of the two arms, which may be reflected in the level of the retracted position.